A measuring device of the type mentioned above is already known from the publication "Kraus et al, BIOSCOPE 1993, No. 1, Pages 24 to 33". Although this measuring device is field-proven in practice, particularly due to its quick response time and the possibility of carrying out selective measurements in the analyte, it nevertheless presents drawbacks. Thus, the function-preserving immobilization of the receptor cells and/or target cells on the physical component of the sensor is extremely critical. One possibility of bringing the receptor cells or target cells into contact with the measurement structure of the measuring device consists, by way of example, in fixing the receptor cells and/or target cells on the measurement structure in an immobile fashion with a gel. This has the drawback, however, that the receptor cells and/or target cells are prestimulated and by this means supply only a comparatively faint signal upon contact with a substance to be detected. Another possibility of bringing the receptor cells and/or target cells into contact with the measurement structure consists in attaching the receptor cells and/or target cells to the measurement structure by mechanical means, for instance using a micromanipulator. This method is, however, comparatively complex, because the micromanipulator has to be manually positioned on the cells under a microscope. In addition, the size of the measuring device, which as such is very compact, is significantly increased by adding the micromanipulator.
A measuring device is also already known where the cells under investigation are contained in a biological buffer medium and where an auxiliary reagent is added to this buffer medium and, when certain chemical components are present, causes coloration of the buffer medium. Thus, by way of example, a calcium colorant can be contained in the buffer medium for detection of calcium ions. For measurement of a change in color brought about by the substance to be detected, the known measuring device has an optical sensor and a light source for transmitting light through the buffer medium. A drawback of this measuring device is particularly that it is of some size and is therefore not sufficiently versatile in use for certain measurements. In addition, the measurement is not free from reactive effect, since some of the auxiliary reagents required are toxic and influence the cells under investigation or the cellular targets. The high photon densities can also lead to changes in the measurement system.
In addition, sensors on enzymatic basis or with microbial structure are known. However, they permit only a single signal analysis, i.e. these sensors always measure only one analyte. What is more, such sensors are vulnerable, because the measurement of a spurious signal does not permit any dependable analyte recognition.